Solar Basics

 

Today we are going to cover the basics about our sun! The sun is a star, and it's the only star associated with our solar system. It's about 93million miles away from Earth, and about 110x the size of Earth. The sun is a giant ball of gas, and has a temperature of over 5800 degrees! It's corona, or surrounding gaseous "atmosphere", can get up to 2 million degrees! The suns composition is about 3/4 hydrogen, 1/4 helium, and a tiny fraction is elements heavier than helium. Fusion reactions of hydrogen into helium in the suns core release energy, which is why the sun emits light. All stars have fusion in their cores and therefore emit light. Objects such as moons and planets do not emit their own light, they reflect light from a nearby star. The sun is about 5 billion years old, and will survive for another 5 billion years. At this point, the sun will expand, engulfing the inner planets, and then shed its outer layers and create a planetary nebula. (But don't worry, that's many years away!) The image above is what the sun looks like today! (For more fun facts about the sun, see the post entitled Our Friend, the Sun)

Image credit: SOHO/ESA/NASA

A "Not So Amateur" Image of the Disk Around Beta Pictoris

We've discussed circumstellar disks around young stars multiple times in this blog, but we haven't discussed how they are observed. Circumstellar disks are best visible at infrared and optical wavelengths. This is because the disks are made of dust and gas, which reflect optical starlight and emit thermal infrared light. Astronomers have used telescopes such as Hubble (optical) and Spitzer (infrared) to image  many disks of young stars, but you don't necessarily need a space telescope to see these disks.  An amateur astronomer named Ralf Olsen proved this by imaging the disk around the nearby young star Beta Pictoris! Armed with his backyard 10inch telescope, a PC webcam and no filters, Olsen was able to image the disk of Beta Pictoris by following a procedure outlined in a 1993 paper by Lecavelier Des Etangs and collaborators. Basically, Olsen imaged Beta Pictoris and a very similar star called Alpha Pictoris, then subtracted the Alpha image from the Beta. Since the stars have similar properties, subtracting the images effectively erased the light of Beta Pictoris, making its disk visible. The image below is the final result from Olsen.

 

The black circle is where Beta Pictoris was removed in the image, and its disk is the extended white region near the star that the dotted lines point to. It's really amazing what an amateur astronomer can do with a basic telescope! Olsen is living proof that you don't need to be a rocket scientist to understand, and even contribute research to the field of astronomy!

Image Credit: Rolf Olsen

http://www.pbase.com/rolfolsen/image/139722640/original

The Slingshot Maneuver

Getting spacecrafts from one planet to another is no easy task. Sure it may sound easy, just fire off a rocket aimed towards the planet of your choice and eventually you will get there. There are many problems with this "point and shoot" method. One is that you would need a lot of fuel to rocket yourself  all the way from Earth to another planet, both to get you there and to keep the ship aimed properly. The more rocket fuel you have though, the harder it is to successfully launch yourself away from Earth, and the more money it costs to fly the space craft. The second major problem comes about once you've reached your destination. Assume you've aimed properly and had enough fuel to make it to the planet in question, now how do you slow down so that you can either safely land on the planet's surface, or orbit it in a stable orbit? More fuel, high tech gadgets, and lot of luck are needed to succeed then. So how do astronomers get spacecrafts from one planet to another? They use the sun! Since the sun is such a massive body, it can be used both to slow spacecrafts down, or speed them up. This is called a gravity assist or slingshot maneuver. When we want to get to Venus or mercury for example, we send spacecrafts around the sun multiple times. The gravitational attraction between the two objects slows the spacecraft down so that it can casually approach the planets. When we want to travel to Jupiter, or the outer edges of our solar system, we use the sun as a slingshot! By sending spacecrafts around the sun at the right distance, the pull of the sun can give the craft angular momentum and increases its speed. As the craft rounds the sun it shot out towards to outer solar system. The key here is to approach the sun with the correct speed, distance and angle, so you get the increase or decrease in speed you desire. Below is the path the Cassini-Huygens mission took around the sun before it was shot out towards Saturn. Carefully planned gravity assists via the sun and inner planets are what got Cassini to Saturn successfully.

 Image Credit: NASA